The present invention relates to a process for preparing a planographic printing plate for an ink-jet recording system, and especially, to a process for preparing a printing plate for a hot melt type ink-jet system which is satisfactory in image quality of both the printing plate and printed matter.
On account of the latest progress in office appliances and office automation, an offset planographic printing system spreads throughout the small printing field, in which a printing plate is prepared, that is, image formation is performed, by various processes from a direct-drawing type planographic printing plate precursor which has on a water-resistant support an image receiving layer having a water-receptive surface.
In conventional direct drawing type planographic printing plate materials, image accepting layers (or image receiving layers) containing inorganic pigments, water-soluble resins, and water resisting enhancers are provided on supports such as paper having undergone a water resistance treatment and plastic films. In known processes for preparing printing plates, lipophilic images are formed on such fresh direct drawing type planographic printing plate precursor by the use of lipophilic ink, with typewriters, by handwriting, by hot melt transfer of images from ink ribbons with heat transfer printers, or by the use of ink-jet printers using a liquid ink.
The printing plates thus prepared, however, fail to have sufficient strength in image areas, which readily causes falling off of the image area on printing.
In platemaking by the ink-jet printers in which a liquid ink is used, in order to prevent image forming agents in the liquid ink from diffusing or absorbing into the plate materials and mitigate blur of images, JP-A-64-27953 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a hot melt type ink-jet process (occasionally referred to as a solid jet process) which uses a hydrophobic solid ink changing to a melted liquid by heating. The image receiving layer of a printing plate precursor used herein has a water-receptive surface.
Even in this process, however, blurs are actually observed in image areas of printed matter obtained from the printing plate thus made, and in addition, the number of sheets which can be printed is insufficient and only a few hundred at most.
The present invention is directed to resolving such problems, and accordingly, an object of the present invention is to provide a process for preparing a printing plate of a hot melt type ink-jet system from which a number of printed sheets having a sharp image can be obtained.
The object given above has been achieved by embodiments of the present invention as described in the following items (1) to (4):
(1) A process for preparing an ink-jet system printing plate, wherein in a planographic printing plate precursor having an image receiving layer containing zinc oxide and a binder resin on a water-resistant support, the surface of the image receiving layer has a water-contact angle of 50xc2x0 or more, and
image formation is carried out according to a hot melt type ink-jet system by heat melting an ink composition that is solid at ordinary temperature and spraying droplets of the ink composition in a hot melt state from a nozzle onto the image receiving layer and a nonimage area of said image receiving layer is then subjected to a desensitizing treatment by a chemical reaction to prepare a planographic printing plate.
(2) A process for preparing the ink-jet system printing forme as described in item (1), wherein the smoothness of the image receiving layer surface of the planographic printing plate is at least 30 seconds per 10 ml in Bekk smoothness degree.
(3) A process for preparing the ink-jet system printing plate as described in item (1), wherein the ink composition contains a wax having a melting point of from 50 to 150xc2x0 C., a resin, a color material, and an adhesion modifier and turns to a hot melted liquid by heating the ink composition to 80xc2x0 C. or more, the hot melted liquid having a viscosity of from 1 to 20 cps.
(4) A process for preparing the ink-jet system printing plate as described in item (1), wherein the smoothness of the support surface adjacent to the image receiving layer is at least 300 seconds per 10 ml in Bekk smoothness degree.